Ultrasound operates by creating an image from sound in three steps—producing a sound wave, receiving echoes, and interpreting those echoes to create an image.
Ultrasound has many uses in medical applications. For example, ultrasound is routinely used during pregnancy to provide images of the fetus in the womb. Generally, a water-based gel is applied to the patient's skin, and a hand-held probe, called a transducer, is placed directly on and moved over the patient. The probe typically contains a piezoelectric element that vibrates and generates a sound wave when a current is applied. In ultrasound devices, the sound wave is typically produced by creating short, strong vibrational pulses using the piezoelectric transducer. The sound wave is reflected from tissues and structures and returns an echo, which vibrates the transducer elements and turns the vibration into electrical pulses. The electrical pulses are then sent to an ultrasound scanner having a display where they are transformed into a viewable analog or digital image on the display.
While general-purpose ultrasound machines may be used for most imaging purposes, certain procedures require specialized apparatus. For example, in a pelvic ultrasound, organs of the pelvic region can be imaged using either external or internal ultrasound. In contrast, echocardiography, which is used in cardiac procedures, can require specialized machines to take into account the dynamic nature of the heart.
Ultrasound has advantages over other imaging methods such as magnetic resonance imaging (MRI) and computed tomography (CT). For example, ultrasound is relatively inexpensive compared to those techniques. Ultrasound also is capable of imaging muscle and soft tissue very well, can delineate interfaces between solid and fluid filled spaces, and may show the structure of organs. Ultrasound renders live images and can be used to view the operation of organs in real time. Ultrasound has no known long-term side effects and generally causes little to no discomfort to a patient. Further, ultrasound equipment is widely available, flexible and portable.
However, ultrasound does have some drawbacks. When used on obese patients, image quality is compromised as the overlying adipose tissue scatters the sound and the sound waves are required to travel greater depths, resulting in signal weakening on transmission and reflection back to the transducer. Even in non-obese patients, depth penetration is limited, thereby making it difficult to image structures located deep within the body. Further, ultrasound has trouble penetrating bone and, thus, for example, ultrasound imaging of the brain within skull bone is limited from external to an animal body. Ultrasound also does not perform well when there is gas present (as in the gastrointestinal tract and lungs). Still further, a highly skilled and experienced ultrasound operator is necessary to obtain quality images. These drawbacks do not, however, limit the usefulness of ultrasound as a medical diagnostic and treatment tool.
The use of ultrasonic apparatus for imaging areas of the human body, either alone or in combination with other instruments, is known, for example, for guiding therapeutic instruments through a catheter to a field of view within a human body. For example, ultrasound devices have been combined with catheters for insertion into a body, usually through a vein or artery, to reach a part of the human body for examination or treatment. Such devices are commonly known in the art as “imaging catheters.”
For example, U.S. Pat. No. 5,704,361 to Seward et al. discloses a volumetric image ultrasound transducer underfluid catheter system. For example, FIGS. 2-9 and 11-12 of Seward et al. and their attendant description suggest specific methods of intervention for imaging purposes in the vicinity of a human heart. To reach such an area of interest within a human body, an ultrasound imaging and hemodynamic catheter may be advanced via the superior vena cava to a tricuspid valve annulus. A distal end of a cylindrical body includes a guide wire access port and a guide wire provides a means of assuring that the catheter reaches a target for imaging. A surgical tool may be fed through the catheter to the area imaged.
U.S. Pat. No. 6,572,551 to Smith et al. provides another example of an imaging catheter. Tools such as a suction device, guide wire, or an ablation electrode, may be incorporated in an exemplary catheter according to Smith et al.
U.S. Pat. No. 5,967,984 to Chu et al. describes an ultrasound imaging catheter with a cutting element which may be an electrode wire or a laser fiber. FIGS. 1 and 2 of Chu et al. also describe a balloon 14 and a means to inflate the balloon. The balloon, for example, may be utilized to dilate a vessel having strictures imaged via the imaging catheter.
Other imaging catheters are known. For example, U.S. Pat. No. 6,162,179 to Moore teaches bending (using a pull wire) an acoustic window into a known and repeatable arc for improved three dimensional imaging. U.S. Pat. No. 6,306,097 to Park et al. discloses an intravascular ultrasound imaging catheter whereby a first lumen provides access for an ultrasound imaging catheter and a second lumen provides a working port for a tool. U.S. Pat. No. 5,505,088 to Chandraratna et al. teaches using a 200 MHz transducer in an ultrasonic microscope combined with a catheter as a delivery means for the microscope to provide imaging of myocardial tissue. According to Chandraratna et al., lower frequency ultrasound transducers can provide deeper penetration in the tissue but do not provide the image quality provided by higher frequencies.
All the above-cited references are incorporated by reference as to any description which may be deemed essential to an understanding of illustrated and discussed aspects and embodiments of devices and methods herein and as summarized below.